Question

Write the IUPAC name of the following complex: \[ K_3[Cr(C_2O_4)_3] \]

Hint:

Negative complex → metal name ends with “-ate”. Fe → Ferrate, Cu → Cuprate, Cr → Chromate.

Answer 1

Step 1: Identify the complex ion. The complex ion is: \[ [Cr(C_2O_4)_3]^{3-} \] since three \( K^+ \) ions balance the charge.
Step 2: Identify ligands. Ligand \( C_2O_4^{2-} \) is called
oxalato. Number of ligands = 3 → prefix =
tris (used for polydentate ligands).
Step 3: Find oxidation state of Cr. Let oxidation state of Cr = \( x \) \[ x + 3(-2) = -3 \] \[ x - 6 = -3 \Rightarrow x = +3 \]
Step 4: Naming the complex.

• Ligand: tris(oxalato)
• Metal: chromium
• Oxidation state: (III)
• Negative complex → metal name ends with “-ate”

So chromium becomes
chromate.
Step 5: Add counter ion. Cation present: Potassium
Final Name: \[ \boxed{\text{Potassium tris(oxalato)chromate(III)}} \]